A depth image sensor with a loaded architecture

Abstract

The invention relates to a sensor comprising at least one depth pixel. A controllable storage area includes a charge flow path extending above a photosensitive region and comprising a memory region separated from the photosensitive region by a potential barrier; a transfer grid opposite the barrier; and a reverse transfer grid opposite the barrier and an upper portion of the photosensitive region. An additional charge flow path extends above the photosensitive region and comprises a collection area separated from the photosensitive region by a collection channel controllable by an initialization grid. A circuit is configured to: sample a signal received in the memory region; initialize a read node; activate the reverse transfer and initialization grids to discharge memory charges; and read an electrical potential from the read node. (See Figure 2A for the abstract.)

Description

Title of the invention: Depth image sensor with a charged architecture. Technical field

[0001] The field of the invention is that of depth image sensors operating on an indirect time-of-flight measurement principle. PREVIOUS STATE OF THE ART

[0002] Depth image sensors make it possible to obtain a three-dimensional image of a scene. Among these are depth image sensors operating on an indirect time-of-flight measurement principle, generally called "iToF image sensors" (iToF for "Indirect Time of Flight"). Such a depth image sensor typically comprises a depth pixel array. It is associated with a light source, for example a laser, to illuminate the scene. The light source emits a periodic light signal in amplitude, often sinusoidal. A pixel, or a group of contiguous pixels corresponding to a point in the image, samples the periodic signal received after reflection from the scene. The sensor includes processing means for determining a phase shift between the emitted and received periodic signals, and for converting the phase shift into a distance separating the image sensor from the scene point conjugate with the image point.

[0003] It is generally accepted that at least three samples over one period of the periodic signal are necessary to perform a distance measurement. It is preferable to use at least four samples. A sample is an integration of the periodic signal received by a pixel over one or more time periods, each equal to a fraction of the period of the periodic signal, the time periods being separated by one period of the periodic signal. Preferably, the fraction of the period of the periodic signal is the same for all samples, for example, equal to the inverse of the number of samples. Generally, the integration time periods of distinct samples do not overlap.

[0004] A depth pixel typically comprises a photosensitive region configured to convert photons of the received light signal into electrical charges, as well as a transfer transistor and a readout node for each sampling branch or for multiple sampling branches. The transfer transistor transfers electrical charges from the photosensitive region to the readout node during time periods corresponding to one sample.

[0005] Among depth pixels operating on an indirect time-of-flight measurement principle, two families are distinguished, namely charge architectures and voltage architectures.

[0006] In a depth pixel according to a voltage architecture, the readout node is directly connected to a source or drain of the transfer transistor. The transfer transistor switches to the conducting state during the integration time periods of a sample. Thus, photogenerated charges accumulate on the readout node during a sampling phase, varying a sampling potential of the readout node. The sampling potential is then read at the end of the sampling phase. The readout node must be reset between each sample. It can be reset to an initialization potential at the beginning of the sampling phase and / or after the sampling potential has been read. The reading of the sampling potential is compared to a reading of the initialization potential on the readout node to determine the sample value.However, resetting the read node adds thermal noise to the initialization potential, commonly called kTC noise, which affects the sample value in this type of architecture.

[0007] A load-based architecture allows the implementation of a kTC noise reduction technique known as correlated double sampling (CDS). A depth pixel in a load-based architecture comprises a memory and a second transfer transistor for each sampling branch, arranged between the transfer transistor and the read node. The memory is therefore separated from the read node by the channel of the second transfer transistor. An example of a depth pixel exhibiting a load-based architecture is given in US patent 2019 / 0086519.

[0008] The photogenerated charges accumulate in the memory during the integration time periods of a sample. At the end of the sampling phase, the read node is reset to an initialization potential, which is read before the electrical charges stored in the memory are transferred to the read node by activating the second transfer transistor. A reading of the read node's potential after transfer is subtracted from the read value of the initialization potential to obtain the sample value. Since the two readings are performed immediately after each other, without switching a switch, the kTC noise is correlated and is therefore eliminated during the subtraction.

[0009] For a load-based architecture, however, memory is bulky and often occupies a blind spot in the depth pixel. Reducing its footprint is undesirable, as it risks compromising sample detection dynamics, that is, the maximum difference between two sample values ​​that The depth pixel or image sensor can record simultaneously. This constraint is further exacerbated when the size of the depth pixel is reduced to increase sensor resolution, or when the photosensitive region is large to increase sensitivity.

[0010] There are specific image sensors, often called RGBZ sensors, that allow for obtaining an intensity image of a scene containing distance information between the sensor and the scene. Such sensors generally comprise a plurality of pixel blocks, each pixel block including an image group of at least one intensity pixel and a macro-pixel Z of at least one depth pixel. The image group is configured to provide intensity information for an observed scene. The macro-pixel Z is configured to provide distance information between the scene and the sensor. In an RGBZ sensor, the image group typically consists of three intensity pixels, one pixel sensitive to red, one to green, and one to blue. The entire set of pixels is arranged in a matrix. It is therefore preferable that the depth pixels be approximately the same size as the intensity pixels.It is therefore desirable that the size of the depth pixels follow the same trend of reduction as the intensity pixels. This often makes the adoption of a load-based architecture difficult, if not impossible.

[0011] There is therefore a need for a more compact depth pixel and / or a new depth pixel architecture enabling correlated dual sampling, without compromising depth pixel size, resolution or image sensor sensitivity. Description of the invention

[0012] The invention aims to remedy at least in part the disadvantages of the prior art, and more particularly to propose an image sensor comprising a plurality of pixels of which at least one is a depth pixel more compact than the depth pixels of the prior art.

[0013] To this end, the object of the invention is an image sensor comprising a readout circuit and a plurality of pixels formed in and / or on a semiconductor substrate of the sensor, such that at least one of the pixels is a depth pixel. Each depth pixel comprises a photosensitive region of the substrate and a controllable storage area.

[0014] The controllable storage area comprises an electrical charge flow path extending vertically in the substrate above the photosensitive region and including a potential well called the memory region and a potential barrier called the barrier interposed between the memory region and the photosensitive region; a transfer grid extending vertically in the substrate at the vertical axis of the photosensitive region, opposite the barrier; a reverse transfer grid extending vertically into the substrate opposite the barrier and an upper part of the photosensitive region.

[0015] Each depth pixel further comprises an additional electric charge flow path extending vertically in the substrate above the photosensitive region comprising a potential well called a collection zone and a potential barrier, called a collection channel, interposed between the collection zone and the photosensitive region.

[0016] Each depth pixel further comprises an initialization grid extending vertically in the substrate directly above the photosensitive region, opposite the collection channel.

[0017] The read circuit includes a read node electrically connected to the collection area. It is configured to successively: apply a periodic pulse train to the transfer gate during a sampling phase so as to flow electrical charges from the photosensitive region to the memory region during the pulses; initialize the read node; activate the inverse transfer gate and the initialization gate so as to flow electrical charges from the memory region to the collection area during a charge evacuation phase; read an electrical potential Vsig from the read node.

[0018] Some preferred but not limiting aspects of this sensor are the following.

[0019] The reading circuit can be configured to read an electrical potential Vinit from the reading node prior to the charge evacuation phase and subsequent to the initialization of the reading node, the sensor being able to be such that it includes means to operate double correlated sampling from Vinit and Vsig.

[0020] The flow path of the controllable storage area may include a pinch zone covering the memory region on one side of the memory region opposite the barrier. The controllable storage area may include a pinch grid that can extend vertically into the substrate opposite the memory region. The read circuit may be configured to apply an electrical potential difference between the pinch zone and the pinch grid so as to passivate the memory region from electrical charges originating from the pinch zone.

[0021] The pinching grid can be housed in a notch made in the reverse transfer grid.

[0022] The reading circuit can further be configured to activate the transfer grid during the charge evacuation phase after the activation of the reverse transfer grid.

[0023] The reading circuit can be configured to activate the initialization grid in opposite phase to the transfer grid during the sampling phase.

[0024] For each pixel of depth, the transfer grid can extend alongside the memory region.

[0025] For each pixel depth, the barrier, the memory region, and the collection area can be doped with a first type of conductivity. They can have dopant element concentrations respectively equal to NI, N2, and N3. NI can be strictly less than N2. N2 can be strictly less than N3.

[0026] For each pixel of depth, the pinch zone can be doped with a second type of conductivity opposite to the first type of conductivity.

[0027] The collection channel may have a concentration of doping elements equal to NI.

[0028] For each pixel of depth, the transfer grid can have a U-shaped shape in top view, surrounding the flow path of the controllable storage area.

[0029] The plurality of pixels can be arranged in a matrix. Each pixel can have a peripheral isolation trench extending vertically in a peripheral region of the pixel opposite a photosensitive region of the pixel. The readout circuit can be configured to apply a common fixed electrical potential to all the peripheral isolation trenches.

[0030] Each pinch grid and each inverse transfer grid can be arranged in separation planes of two contiguous pixels of the pixel matrix.

[0031] The peripheral isolation trenches can form a continuous mesh comprising cells such that each cell surrounds two pixels. The reading circuit can be electrically connected to a peripheral area of ​​the mesh so as to apply a common fixed electrical potential.

[0032] All pixels in the matrix can have the same size. The pixel matrix can include intensity pixels configured to deliver a signal representative of the intensity of an incident luminous flux. Brief description of the drawings

[0033] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0034] [Fig.1A] is a schematic top view of an example of a depth pixel according to the invention;

[0035] [Fig.1B] is a schematic view along section AA of [Fig.1A] of the example depth pixel;

[0036] [Fig.2A] is an electrical diagram of a reading circuit adapted to the depth pixel of figures IA and IB;

[0037] [Fig.2B] is a timing diagram illustrating a possible operation of the reading circuit;

[0038] Figures 3A to 3D illustrate variations in electrical potentials within the depth pixel of Figures IA and IB;

[0039] [Fig.4] is a partial schematic, top view of a depth pixel matrix;

[0040] [Fig.5] is a partial schematic, top view of a pixel matrix mixing intensity pixels and depth pixels;

[0041] [Fig.6] is a schematic view along section AA of [Fig.5] or [Fig.6].

[0042] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0043] In the figures and in the following description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are inclusive, unless otherwise stated.

[0044] The invention relates to an image sensor. The sensor comprises a substrate, a readout circuit, and a plurality of pixels formed in and / or on the substrate. At least one pixel among the plurality of pixels is a depth pixel.

[0045] Each depth pixel comprises a photosensitive region and a controllable storage area arranged directly above the photosensitive region. The controllable storage area comprises an electrical charge flow path, a transfer grid, and a reverse transfer grid. The flow path includes a memory region separated from the photosensitive region by a barrier.

[0046] Each depth pixel further comprises an additional channel for the flow of electrical charges, also arranged directly above the photosensitive region, comprising a collection zone separated from the photosensitive region by a potential barrier called a collection channel.

[0047] The grids extend vertically into the substrate. The transfer grid is directly above the photosensitive region. A readout node of the readout circuit is electrically connected to the collection zone. The transfer grid and the reverse transfer grid extend opposite the barrier, so that the barrier can be controlled by either the transfer grid or the reverse transfer grid, or by both simultaneously. The reverse transfer grid also extends opposite an upper portion of the photosensitive region, so that it can to change sign a difference in electrical potentials between the memory region and the photosensitive region.

[0048] This arrangement, in combination with a specific configuration of the readout circuit, allows the storage area to be controlled in such a way as to permit a bidirectional flow of electrical charges in the flow path. It is thus possible to accumulate photogenerated electrical charges in the memory region during a sampling phase and to discharge them during a readout phase to the collection area. An electrical potential of the readout node is then read by the readout circuit. This corresponds to the number of charges accumulated and subsequently transferred. The memory region thus emptied can serve as a receptacle for a new sampling phase.

[0049] In operation, the photosensitive region is designed to receive electromagnetic radiation incident on an underside of the substrate opposite the controllable storage area. Thus, the depth pixel is compact and has few or no blind spots.

[0050] Specific embodiments will be described relating to an image sensor comprising a readout circuit based on NMOS transistors. However, these embodiments can be adapted to other types of readout circuits, allowing the technical aspects of the description to be implemented without departing from the scope of the invention. For example, it is possible to use a readout circuit based on PMOS transistors or on a combination of NMOS and PMOS transistors.

[0051] Similarly, each embodiment described below adopts a particular combination of conductivities associated with the doped areas, it being understood that the combination can be reversed without departing from the scope of the invention. Thus, for a particular embodiment, all P-doped areas can be N-doped and all N-doped areas can be P-doped, provided that the type of conductivity of all the doped areas is changed. The examples of electrical potentials or bias voltages given in the description are given relative to the particular combination of conductivities and doping concentrations used for the example embodiments, in association with an example of an NMOS readout circuit. It is within the scope of those skilled in the art to establish the electrical potentials and / or bias voltages suitable for other possible combinations within the scope of the invention.

[0052] An example of a pixel depth 5 of an image sensor according to the invention will now be described with reference to Figures IA and IB. Figures IA and IB are schematic top and cross-sectional views, respectively. The cross-sectional plane of [Fig. 1B] is represented by a dashed line on [Fig. 1A].

[0053] An image sensor comprises a readout circuit and a plurality of pixels formed in and on a substrate 100, at least one of which is a pixel with a depth of 5. In Figures IA to IB, only one pixel with a depth of 5 of the sensor is shown. To avoid cluttering the diagrams, certain elements have been omitted, such as interconnecting lines or certain electrical contacts. To improve readability, only the upper part of the substrate 100 is shown in the cross-sectional view. In the schematic views, the elements are represented by simple geometric shapes. These are reproduced on the manufactured device, with manufacturing errors such as misalignment, dimensional errors, or rounded corners due to insufficient resolution.

[0054] The substrate 100 has an upper face 100.1 and a lower face opposite the upper face 100.1. The lower and upper faces 100.1 are substantially flat and parallel to each other. The pixel at depth 5 includes a photosensitive region 120 and a controllable storage area. The controllable storage area includes a flow path. The flow path includes a barrier 131, a memory region 135, and a pinch zone 121.

[0055] The pixel at depth 5 further comprises an additional flow path and an initialization grid 113. The additional flow path includes a collection zone 125 and a collection channel 133. In this example, the pinch zone 121 and the collection zone 125 are flush with the top face 100.1. The flow path of the controllable storage zone and the additional flow path extend vertically in the substrate 100 above the photosensitive region 120, between the photosensitive region 120 and the top face 100.1 of the substrate 100.

[0056] A three-dimensional orthogonal (X, Y, Z) direct coordinate system is defined herein and for the remainder of this description, where the X and Y axes form a plane parallel to the upper face 100.1 of the substrate 100, the X axis being oriented in the cutting plane AA, and where the Z axis is oriented substantially orthogonally to the upper face 100.1, from the photosensitive region 120 towards the upper face 100.1. In the remainder of this description, the terms "vertical" and "vertically" are understood to refer to an orientation substantially parallel to the Z axis, and the terms "horizontal" and "horizontally" to refer to an orientation substantially parallel to the (X, Y) plane. Furthermore, the terms "lower" and "upper" are understood to refer to an increasing positioning as one moves away from the upper face 100.1 of the substrate 100, along the +Z direction. The term "lateral" refers to an orientation substantially parallel to the Z-axis.

[0057] The substrate 100 is made of a semiconductor material. Here it is crystalline silicon. For example, it is a silicon wafer or part of a silicon wafer. It may include one or more epitaxial layers of crystalline silicon, as well as one or more passivation layers.

[0058] The barrier 131 is arranged between the photosensitive region 120 and the memory region 135. The barrier 131 constitutes an electrical potential barrier for electrical charges intended to be photogenerated in the photosensitive region 120. The photogenerated electrical charges are electrons from a conduction band of the photosensitive region 120. The memory region 135 constitutes an electrical potential well for the photogenerated electrical charges.

[0059] The pinch zone 121 covers the memory region 135, on one side of the memory region 135 opposite the barrier 131. The pinch zone 121 preferably completely covers the memory region 135. The controllable storage area further comprises a pinch grid 114. The pinch grid 114 extends vertically in the substrate 100 opposite the memory region 135. The pinch zone 121 and / or the pinch grid 114 are intended to fix an electrical potential, called the pinch potential, of the memory region 135. Preferably, the pinch zone 121 and / or the pinch grid 114 are intended to deplete the memory region 135 in the absence of photogenerated electrical charges.

[0060] The controllable storage area further comprises a transfer grid 111, a reverse transfer grid 112. The transfer grid 111 extends vertically in the substrate 100 above the photosensitive region 120 between the upper face 100.1 and the photosensitive region 120. It extends opposite the barrier 131. Preferably, as is the case here, it extends vertically opposite the memory region 135.

[0061] The inverse transfer grid 112 extends vertically within the substrate 100 opposite the barrier 131 and an upper portion of the photosensitive region 120, preferably opposite the entire photosensitive region 120. Advantageously, the inverse transfer grid 112 extends substantially to the lower face of the substrate 100. Here, it delimits the photosensitive region 120 in a horizontal plane. In a top view, it completely surrounds the photosensitive region 120 and has a closed contour, here substantially square in shape, with sides parallel to the X-axis or the Y-axis. In a plane parallel to the upper face 100, the distance Px separating an outer edge of one side of the square from an inner edge of the opposite side of the square defines a pixel size. In this example, the pixel size Px is equal to 1.2 pm. It can be less than or equal to 1.2 pm, or even less than or equal to 1 pm.

[0062] One or more horizontal distances separating the transfer grid 111 from the reverse transfer grid 112 at the barrier 131 and a concentration of dopant elements in the barrier 131 are such as to create an electrical potential barrier at the barrier 131, between the photosensitive region 120 and the memory region 135. Similarly, one or more horizontal distances separating the transfer grid 111 from the pinch grid 114 and a concentration of dopant elements in the memory region 135 are such as to create an electrical potential well at the level of the memory region 135, between the barrier 131 and the pinch zone 121. The transfer grid 111 and the inverse transfer grid 112 are opposite each other at the level of the barrier 131 so that the latter can be controlled indifferently by either of the transfer grid 111 or the inverse transfer grid 112, or simultaneously by both.

[0063] In this example, the photosensitive region 120, the barrier 131, and the memory region 135 are doped with a first type of conductivity. Here, the first type of conductivity is n-type. The barrier 131 and the memory region 135 have doping element concentrations equal to NI and N2, respectively, such that NI is strictly less than N2.

[0064] The barrier 131 extends horizontally from the transfer grid 111 to the reverse transfer grid 112. The memory region 135 extends horizontally from the transfer grid 111 to the pinch grid 114. Here, the pinch grid 114 occupies a notch made in the reverse transfer grid 112. It is substantially flat.

[0065] The collection channel 133 is arranged between the photosensitive region 120 and the collection zone 125. The collection channel 133 constitutes an electrical potential barrier for the electrical charges intended to be photogenerated in the photosensitive region 120. The collection zone 125 constitutes an electrical potential sink for the photogenerated electrical charges.

[0066] The initialization grid 113 extends vertically in the substrate 100 directly above the photosensitive region 120, opposite the collection channel 133. Here, the inverse transfer grid 112 extends vertically opposite the collection channel 133. Optionally, as shown here, the depth pixel 5 may include an additional pinch grid 114 extending vertically opposite the collection area 125. In this example, the additional pinch grid 114 has all its dimensions identical to the pinch grid 114 of the controllable storage area. The two pinch grids 114 are symmetrical to each other with respect to a plane of symmetry parallel to the (Y, Z) plane passing through the center of the depth pixel 5. The inverse transfer grid 112 is symmetrical with respect to this plane. The additional pinch grid 114 can extend opposite the collection channel 133, in part or in full.

[0067] One or more horizontal distances separating the initialization grid 113 from the reverse transfer grid 112 at the level of the collection channel 133 and a concentration of doping elements in the collection channel 133 are such as to create a barrier of electrical potential at the level of the collection channel 133, between the photosensitive region 120 and the collection zone 125. Similarly, one or more horizontal distances separating the initialization grid 113 from the additional pinching grid 114 and a concentration of doping elements in the collection channel 133 are such as to create an electrical potential well at the level of the collection zone 125 and an electrical potential barrier between the photosensitive region 120 and the collection zone 125.

[0068] In this example, the collection channel 133 and the collection zone 125 are doped with the first type of conductivity. The collection zone 125 has a doping element concentration equal to N3, such that N2 is strictly less than N3. The collection channel 133 may have a doping element concentration equal to that of the barrier 131, as is the case in this example. If so, the doping of the collection channel 133 and the barrier 131 may result from in-situ doping during epitaxial growth. Epitaxial growth may include the formation of the photosensitive region 120.

[0069] The collection channel 133 extends horizontally from the initialization grid 113 to the reverse transfer grid 112. The collection area 125 extends horizontally from the initialization grid 113 to the additional pinching grid 114.

[0070] All the grids of the pixel at depth 5, among a set of grids consisting of the transfer grid 111, the inverse transfer grid 112, the pinch grid 114, the additional pinch grid 114, and the initialization grid 113, may each be flush with the upper face 100.1 of the substrate 100, although this is not essential. Each grid in the set of grids has an electrode 102 made of an electrically conductive material, such as a metal or a doped semiconductor. The electrodes 102 are advantageously made of the same material. Here, they are all made of doped polycrystalline silicon. They are doped with a second type of conductivity opposite to the first type of conductivity, that is, p-doped in this example.

[0071] The photosensitive region 120 can be doped or intrinsic. A geometry of the inverse transfer grid 112 and a concentration of doping elements in the photosensitive region 120 are such that the memory region 135 has an electrical potential intermediate between the electrical potential of the photosensitive region 120 and the electrical potential of the collection zone 125, when all the grids in the grid assembly are at the same electrical potential. The electrical potential of the photosensitive region 120 can be equal to the electrical potential of the memory region 135.

[0072] The electrode 102 of each grid in the grid assembly is coated with a dielectric coating 129 of the grid. The dielectric coatings 129 are made of any dielectric material. Here, they are made of silicon oxide. Each grid is electrically insulated from the semiconductor substrate 100 by a dielectric coating 129. A coating dielectric 129 electrically isolates electrode 102 of pinch grid 114 from electrode 102 of reverse transfer grid 112, as well as electrode 102 of additional pinch grid 114 from electrode 102 of reverse transfer grid 112.

[0073] The transfer grids 111 and initialization grids 113 each have an insulating region 139 covering their respective electrodes 102 and flush with the upper face 100.1 of the substrate 100. The insulating regions 139 are made of any dielectric material. Here they are made of silicon oxide.

[0074] The pinch zone 121 is doped with the second type of conductivity, p-doped in this example. It advantageously comprises a peripheral doped zone 141 extending horizontally into a peripheral region of the pixel with a depth of 5. The pinch zone 121 has a concentration PI of dopant elements. It can extend deeper into the substrate 100 at the level of its peripheral doped zone 141. In this example, it extends vertically into the substrate 100 to a substantially constant depth, for example, greater than or equal to a height along the Z-axis of the insulating regions 139. The pinch zone 121 with its peripheral doped zone 141 can, for example, be obtained by a single localized implantation step. Here, the peripheral doped zone 141 surrounds the transfer grid 111 and the initialization grid 113.It has an outer perimeter in contact over its entire surface with a grid among the pinching grid 114, the additional pinching grid 114 and the reverse transfer grid 112.

[0075] The initialization grid 113 is arranged in the depth pixel 5 so as to screen, in the collection channel 133, an electric field emitted by the transfer grid 111 when the sensor is operating. Similarly, the transfer grid 111 is arranged so as to screen, in the barrier 131, an electric field emitted by the initialization grid 113 when the sensor is operating. This is achieved here by interposing the transfer grid 111 and the initialization grid 113 between the two flow paths. The transfer grid 111 and the initialization grid 113 are separated by a distance S measured parallel to the X-axis, at an inter-grid region 130 of the depth pixel 5. By way of example, the distance S is between 10 nm and 300 nm, here equal to 70 nm. The inter-grid region 130 separating the transfer grid 111 from the initialization grid 113 is made of any dielectric or semiconductor material, doped or undoped.It is here in crystalline silicon. In this example, it is n-doped. It has a concentration of doping elements equal to NI.

[0076] The transfer grid 111 has a U-shaped form in top view, surrounding the flow path. It comprises a main portion forming the base of the U, extending parallel to the (Y, Z) plane, as well as a first and a second branch of the U extending parallel to the (X, Z) plane. In this example, the main portion The first branch and the second branch have horizontal widths approximately equal to a value W. The second branch has a horizontal width strictly greater than W. The horizontal width of the second branch is, for example, sufficient to guarantee that a first contact 161 of the read circuit rests entirely on the second branch despite manufacturing uncertainties. W is equal to 110 nm here. The width of the second branch is equal to 200 nm here. The first and second branches have equal lengths WN, measured parallel to the X-axis. WN is equal to 336 nm here. The first branch is separated from the second branch by a distance LN measured parallel to the Y-axis, equal to 640 nm here.

[0077] The initialization grid 113 is in this example symmetric to the transfer grid 111 by an axial symmetry with respect to a vertical axis of symmetry passing through the center of the pixel of depth 5. The transfer grid 111 and / or the initialization grid 113 can however have other shapes in top view, independently of each other, for example an L-shaped or I-shaped shape, with or without serifs.

[0078] In this example, the inverse transfer grid 112 has a substantially constant horizontal width around its entire perimeter, here equal to 100 nm. The pinch grid 114 and the additional pinch grid 114 are aligned on respective faces of the inverse transfer grid 112. They have a horizontal width equal to that of the inverse transfer grid 112.

[0079] Preferably, the collection zone 125 extends deeper into the substrate 100 from the upper face 100.1 than the insulating regions 139. It extends less deeply than the additional pinch grid 114. The memory region 135 extends deeper from the pinch zone 121 to the barrier 131. The pinch grid 114 extends deeper into the substrate 100 from the upper face 100.1. Preferably, it extends until it substantially reaches a separation plane between the memory region 135 and the barrier 131, within manufacturing uncertainties.

[0080] The respective electrodes 102 of the pinch grid 114 and the reverse transfer grid 112 are insulated from each other by the dielectric coating 129. For example, they are separated by the dielectric coating 129 by a distance between 2 nm and 100 nm, here equal to 20 nm. Similarly, the respective electrodes 102 of the additional pinch grid 114 and the reverse transfer grid 112 are separated by the dielectric coating 129 by an equivalent distance. Here, the dielectric coatings 129 of all the electrodes 102 of the grid assembly have substantially equal thicknesses.

[0081] NI is, for example, between 1E10 at / cm3 and 1E18 at / cm3. N2 is, for example, between 1E16 at / cm3 and 1E19 at / cm3. N3 is, for example, between 1E17 at / cm3 and 5E20 at / cm3. PI is, for example, between 1E17 at / cm3 and 5E20 at / cm3.

[0082] Now, in connection with [Fig. 2A], a sensor readout circuit will be described, adapted to the example of a depth pixel 5 in Figures IA and IB. [Fig. 2A] uses the cross-sectional view of [Fig. 1B] without the reference numerals. Electrical connections linking the various elements of the depth pixel 5 to the readout circuit are schematically represented, but are not necessarily representative of a geometric arrangement in space.

[0083] The reading circuit includes the first contact 161, a second contact 162, a third contact 163, a fourth contact 164, a sixth contact 166, and a seventh contact 167.

[0084] The pinch grids 114 are each electrically connected, via their fourth contact 164, to a node or rail supplying an electrical potential VLO2. The initialization grid 113 is electrically connected, via the third contact 163, to a node or rail supplying an electrical potential TGRST. The reverse transfer grid 112 is electrically connected, via the second contact 162, to a node or rail supplying an electrical potential TGZ. The pinch zone 121 is electrically connected to a node or rail supplying an electrical potential VLO1, via the seventh contact 167.

[0085] The read circuit further includes a transistor 53 mounted as a source follower and a selector transistor 54. Transistors 53 and 54 are NMOS transistors. The drain of transistor 53 is electrically connected to a node or rail supplying an electrical potential VSF. The source of transistor 53 is electrically connected to the drain of the selector transistor 54. The source of the selector transistor 54 is electrically connected to an output line having an electrical potential Vx. The output line is connected to a column foot of the pixel matrix. The gate of the selector transistor 54 is electrically connected to a node or rail supplying an electrical potential RD. The collection area 125 is electrically connected to a read node SN via the sixth contact 166. The read node SN is electrically connected to the gate of transistor 53.It is further electrically connected to a node or rail supplying an electrical potential VRTRST via the channel of an initializer transistor 57 of the readout circuit. The second switch 57 is controlled by an electrical potential RST. This is an NMOS transistor.

[0086] In connection with [Fig. 2B], a possible operation of this reading circuit will be illustrated. [Fig. 2B] represents a timing diagram on which potentials have been plotted electrical currents vary over time. Some of these are identified by solid disks on the electrical diagram in [Fig. 2A]. Different polarization states of the pixel at depth 5 during one cycle of the chronogram have been represented by elementary geometric shapes placed on a timeline.

[0087] Figures 4A to 4D are schematic representations illustrating the evolution of the electrical potential as it passes through various regions of the pixel at depth 5, corresponding to the polarization states identified in [Fig. 2B]. The elementary geometric shape used to identify the corresponding polarization state of the timing diagram is drawn in the upper left corner of each of Figures 4A to 4D. In these figures, the y-axis gives the value of the electrical potential, in arbitrary units, at a position of the pixel at depth 5 located on the x-axis. The different regions of the pixel at depth 5 are identified by vertical dashed lines and a reference point placed opposite them on the x-axis. The sequence passes successively from the collection zone 125, to the collection channel 133, to the photosensitive region 120, to the barrier 131, to the memory region 135, and finally to the pinch zone 121.

[0088] In each of the figures 3A to 3D, the evolution of the electric potential inside the pixel at depth 5 is schematically represented by a light grey line when the electric potentials TGZ, TGMEM, TGRST, VLO2 are equal to -0.8 V; VLO1 is equal to -0.5 V, and the electric potential of the SN reading node is equal to 1.8 V. A black line schematically represents the evolution of the potential for the corresponding polarization state.

[0089] When a scene is illuminated by a light source emitting a periodic light signal with an amplitude of period Ps, the chronogram leads to an integration of a part of the light signal reflected by the scene, over periodic time intervals of period equal to the period Ps and of duration equal to Ps / 4.

[0090] The timing diagram is adapted to a sensor for an image comprising several pixels of depth 5 arranged in a matrix. It successively includes an initialization phase T0, a sampling phase T1, and a matrix readout phase TM. The matrix readout phase TM consists of an optional first waiting phase T2, a first readout phase T3, a charge evacuation phase T4, a second readout phase T5, and an optional second waiting phase T6. The sum of the consecutive phases T0, T1, and TM constitutes a depth image acquisition phase, or a frame acquisition phase, for example, if the sensor is capable of capturing several successive images. If applicable, the matrix readout phase TM of a frame can be immediately followed by the initialization phase T0 of the next frame.

[0091] In order to determine depth information from the periodic light signal received by the sensor during an image acquisition phase, the pixel A depth 5 pixel can belong to a macro-pixel Z comprising several identical depth 5 pixels. If so, the sampling phases Tl of distinct depth 5 pixels of macro-pixel Z are shifted by a fraction of the period Ps, modulo the period Ps. A macro-pixel Z can, for example, consist of 4 depth 5 pixels whose sampling phases Tl are shifted in pairs by a quarter of the period Ps, modulo the period Ps.

[0092] Alternatively, depth information can be determined from the periodic light signal received by the sensor during successive frame acquisition phases. For example, the sampling phases T1 of successive frames can be shifted by one-quarter of the period Ps modulo the period Ps, or the light signal can be shifted by one-quarter of the period Ps modulo the period Ps from one frame to the next. The depth information is then determined from the samples collected by the depth pixel 5 during the successive frame acquisition phases. Other arrangements are also possible, allowing depth information to be acquired from samples collected over several frames with a macro-pixel Z of at least one depth pixel 5.

[0093] During the image or frame acquisition phase, the electrical potentials VLO1, VLO2, VSF, and VRTRST are fixed. For example, VLO1 is equal to -0.5 V or 0 V. VLO2 is, for example, equal to -0.8 V. VSF is, for example, equal to 1.8 V. VRTRST is, for example, equal to 1.8 V or 2.5 V.

[0094] VL02 is strictly less than VL01 so that holes from the pinch zone 121 are attracted along the pinch grid 114 by an electric field between the pinch zone 121 and the pinch grid 114. Thus, these holes form with the memory region 135 a lateral junction passivating the memory region 135.

[0095] The initialization transistor 57 is kept conducting during the initialization and sampling phases T0, T1, as well as during the first and second waiting phases T2, T6.

[0096] During the initialization phase T0, the photosensitive region 120 and the memory region 135 are cleared of any electrical charges they may contain. For this purpose, the electrical potentials TGRST, TGMEM, and TGZ are initially all equal to a high value VH. The pixel at depth 5 is in a polarization state corresponding to [Fig. 3A], for which the electrical potential of the photosensitive region 120 is strictly greater than the electrical potential of the barrier 131, which is in turn strictly greater than the electrical potential of the memory region 135. Electrons contained in the memory region 135 flow thus, under the action of an electric field between the memory region 135 and the photosensitive region 120, from the memory region 135 towards the photosensitive region 120.

[0097] TGMEM is then switched to a low value VL, while TGRST and TGZ are maintained at the high value VH. In this example, the VL value is -0.8 V. The VH value is 1.8 V. The corresponding polarization state is shown in [Fig. 3C]. In this state, the electrical potential of the barrier 131 is strictly lower than that of the photosensitive region 120, thus preventing electrons from moving from the photosensitive region 120 to the memory region 135. In this state, the electrical potential of the collection channel 133 is preferentially strictly higher than the electrical potential of the barrier 131; therefore, electrical charges that cannot be contained in the photosensitive region 120 when it is at its capacity limit flow towards the collection area 125 rather than into the memory region 135.

[0098] Finally, TGZ is switched to the value VL, while TGMEM and TGRST are maintained at VL and VH respectively. This polarization state corresponds to the situation in [Fig. 3D] where no potential barrier is present between the photosensitive region 120 and the collection area 125. In this case, the electrical potential increases as it passes from the photosensitive region 120 to the collection area 125, via the collection channel 133. Thus, an internal electric field within the pixel, with a depth of 5, drives electrons present in the photosensitive region 120, particularly those from the memory region 135, from the photosensitive region 120 to the collection area 125. At the end of the initialization phase T0, the memory region 135 and the photosensitive region 120 are essentially devoid of free electrical charges; they are said to be initialized. They are at respective electrical potentials, known as pinch potentials.

[0099] During the sampling phase T1, a periodic pulse train is applied to the transfer gate 111. TGMEM is a periodic square wave function with period Ps, between VH and VL. Here, at each period of the square wave function, TGMEM is equal to VH for a duration equal to Ps / 4. During this phase, TGRST switches between VH and VL, in opposite phase to TGMEM. We thus switch from a polarization state illustrated in [Fig.3B], for which photo-generated electrical charges pass from the photosensitive region 120 to the memory region 135 during the pulses, to a polarization state illustrated in [Fig.3D] commented above, for which electrical charges pass from the photosensitive region 120 to the collection area 125. At the end of the sampling phase T1, the memory region 135 contains a quantity of photo-generated electrical charges corresponding to a sample.

[0100] Throughout the sampling phase T1, the light signal is active (reference SL on the timing diagram). Preferably, the light signal SL is only active during the sampling phase TL. Means, such as a clock or a synchronization signal, allow the light signal to be synchronized with the readout circuit. These means may be external to or integrated into the sensor, in whole or in part. Alternatively, the sensor may include means for blocking the light signal reflected by the scene before it reaches the photosensitive region 120, outside the sampling phase TL.

[0101] In [Fig.3B], the electric potential increases when passing from the photosensitive region 120 to the memory region 135, so that an internal electric field generates a displacement of electrons from the photosensitive region 120 to the memory region 135. The electrons are photo-generated electrons by the light signal, that is to say, they are electrons located in the conduction band of the photosensitive region 120 following the absorption of one or more photons of the light signal.

[0102] The first waiting phase T2 is a waiting phase for the selection of the row or column of the matrix to which the pixel at depth 5 belongs. This phase is generally used to read other rows or columns. During this phase, TGZ and TGMEM are equal to VL, while TGRST is equal to VH. This situation is illustrated in [Fig. 3D] and discussed above. It prevents any additional electrical charges generated in the photosensitive region 120 after the sampling phase T1 from being transferred to the memory region 135 between the sampling phase T1 and the reading of the value of the sample collected in the memory region 135 during the sampling phase TL. The additional electrical charges are discharged to the collection area 125. This function is sometimes called anti-blooming.

[0103] The first waiting phase T2 is followed by a first reading phase T3. The first reading phase T3 begins when the selection transistor 54 is switched on (RD to a high value). The initialization transistor 57 is then switched off (RST to a low value). At the moment RST switches, the light signal is already interrupted or blocked so that no electrical charge is photogenerated by the light signal. The reading node SN is thus initialized to an electrical potential Vinit, substantially constant until the end of the first reading phase T3, corresponding to VRTRST plus an electrical potential VkTc corresponding to thermal noise of the reading circuit. The value of the electrical potential Vinit is read on the output line and stored at the column foot. The reading node SN has a capacitance CSN. The capacitance CSN is not necessarily an independent component of the reading circuit.It can be induced by . various factors related to design and materials, such as interconnection lines, one or more transistor gates...

[0104] A charge evacuation phase T4 follows the first readout phase T3. The charge evacuation phase T4 is identical or similar to the initialization phase T0. It begins when TGZ and TGMEM switch to the high value VH, while TGRST remains at VH. Preferably, TGZ switches to VH before TGMEM. The pixel at depth 5 is then in the polarization state shown in [Fig. 3A]. TGMEM is then switched to a low value VL, while TGRST and TGZ remain at the high value VH. The corresponding polarization state is shown in [Fig. 3C]. At the end of the charge evacuation phase T4, TGZ switches to the value VL, while TGMEM and TGRST remain at VL and VH, respectively. This polarization state corresponds to the situation shown in [Fig. 3D].

[0105] Alternatively, TGMEM can be maintained at the low value for the entire duration of the charge evacuation phase T4. TGZ switches from the high value VH (situation of [Fig.3C]) to the low value VL (situation of [Fig.3D]), during the charge evacuation phase T4.

[0106] At the end of the charge evacuation phase T4, the memory region 135 is cleared of the photogenerated electrical charges that had been transferred from the photosensitive region 120 during the sampling phase TL. It returns to its pinch potential. The photogenerated charges reach the collection area 125 and charge the CSN capacitor of the read node SN to an electrical potential Vsig.

[0107] The charge evacuation phase T4 is followed by a second read phase T5. The second read phase T5 begins after switching TGZ to the low value VL, with TGMEM and TGRST being held at VL and VH respectively, it being understood that TGRST could also be equal to VL during the second read phase T5. The value of the electrical potential Vsig is read on the output line and stored at the column foot. Vsig is representative of the number of photogenerated electrical charges collected in the memory region 135 during the sampling phase TL. The second read phase T5 ends when the selection transistor 54 is switched to a blocking state (RD to a low value).

[0108] In this example, the sensor includes means for performing correlated double sampling. These means include, in particular, the first read phase T3, the storage of Vinit read at the column foot, and an analog cell producing a signal proportional to the difference between Vinit and Vsig. The analog cell subtracts Vsig from Vinit, for example. Since the readings of Vinit and Vsig are consecutive, without any change in the state of the initialization transistor 57 between the first and second read phases T3, T5, the reading of Vsig is unaffected. This adds thermal noise to that already present in the Vinit reading. Therefore, subtracting Vsig from Vinit eliminates the kTC noise. The Vsig and Vinit readings are thus said to be correlated.

[0109] The second read phase T5 is followed by an optional second wait phase T6 during which additional rows of the pixel matrix may be selected. The electrical potentials of the timing diagram are at the same values ​​as those of the first wait phase T2. After the second wait phase T6, for example immediately after, the initialization phase T0, the sampling phase T1, and the read phase TM can be repeated to acquire another frame.

[0110] A sensor comprising a pixel array of depth 6 will now be described with reference to [Fig. 4]. All pixels of depth 6 are identical. Each pixel of depth 6 is a variant of the pixel of depth 5 illustrated in Figures IA and IB. Only the differences between this variant and the pixel of depth 5 are explicitly described. [Fig. 6] is a schematic view along section AA of [Fig. 4].

[0111] The inverse transfer grid 112 is planar. It extends along a vertical plane parallel to the (Y, Z) plane. The pixel at depth 6 has no additional pinch grid 114. The pinch grid 114 extends in the same vertical plane as the inverse transfer grid 112. It occupies the notch in the inverse transfer grid 112.

[0112] Each inverse transfer grid 112 and each pinch grid 114 are common to two contiguous pixels of depth 6 in the matrix. These are, for example, symmetrical to each other with respect to the vertical plane along which the inverse transfer grid 112 and the pinch grid 114 extend, as shown here.

[0113] Each pixel of depth 6 has a peripheral isolation trench 115. The peripheral isolation trench 115 extends vertically in a peripheral region of the pixel opposite the additional flow path and the photosensitive region 120. In this example, it has a U-shaped shape in top view surrounding the additional flow path, the photosensitive region 120, the initialization grid 113 and the transfer grid 111. It surrounds the pinch zone 121. Here, it extends from the top face 100.1, preferably to a depth substantially equal to the thickness of the substrate 100.

[0114] In this example, the peripheral isolation trench 115 extends along three consecutive faces of the 6-depth pixel so as to completely cover them. Thus, the peripheral isolation trenches 115 of the matrix of two contiguous 6-depth pixels meet. They form a continuous mesh, such that each cell surrounds two contiguous 6-depth pixels of the matrix.

[0115] The peripheral insulating trench 115 includes a vertical electrode 106 coated with a dielectric coating 129. The vertical electrodes 106 form a continuous, one-piece mesh. The dielectric coating 129 of the peripheral insulating trench 115 electrically insulates the vertical electrode 106 from the substrate 100. Here, the peripheral insulating trench 115 further includes an insulating region 139 covering the vertical electrode 106 and flush with the upper face 100.1 of the substrate 100. The vertical electrode 106 is, for example, made of doped polycrystalline silicon. The dielectric coating 129 is, for example, made of silicon oxide. The insulating region 139 is, for example, made of silicon oxide. The vertical electrode mesh 106 is connected, for example at the periphery of the matrix, to a fixed electrical potential allowing to passivate regions of the pixels of depth 6 opposite the peripheral isolation trenches 115.

[0116] The peripheral doped areas 141 of two pixels of depth 6 in a mesh meet at the plane of the inverse transfer grid 112, to form a single area.

[0117] A sensor comprising a pixel matrix mixing intensity 7 pixels and depth 6 pixels will now be described. Several intensity 7 pixels can be inserted into the pixel matrix. Figure 5 shows a top view of a set of four pixels from the matrix. Figure 6 is a view along section AA of Figure 5. The set of four pixels is, for example, repeated periodically to form the matrix. Here, it comprises three intensity 7 pixels and one depth 6 pixel. Only the differences with the sensor in Figure 4 are explicitly described. The depth and intensity 6 and 7 pixels have superimposable horizontal footprints, meaning that all their horizontal dimensions are equal.

[0118] The depth pixel 6 is identical to that described in connection with [Fig. 4]. Each intensity pixel 7 can be any type of pixel delivering a signal proportional to the intensity of a portion of the electromagnetic radiation from the scene and incident on the underside of the substrate 100, excluding the light signal. The intensity pixel 7 can, for example, be a pixel similar or identical to that described in US patent 2019 / 0237499 AL

[0119] Each intensity pixel 7 comprises a transfer grid 117, a detection zone 126 and a box 127. It also comprises a peripheral isolation trench 115 identical to the depth 6 pixel. The pixel matrix of [Fig.5] is obtained by replacing depth 6 pixels of the matrix of [Fig.4] with intensity 7 pixels. Thus, the peripheral isolation trenches 115 form a mesh identical to that of [Fig.4].

[0120] The detection zone 126 and the housing 127 are doped with opposing types of conductivity. In this example, although not essential, the housing 127 is doped of the same type of conductivity as the pinch zone 121 and its peripheral doped zone 141. The box 127 and the pinch zone 121 may for example result from one or more common implantation steps.

[0121] A first mesh formed by the peripheral isolation trenches 115 surrounds two pixels of intensity 7. A second mesh surrounds a pixel of depth 6 with a pixel of intensity 7. In the first mesh, the boxes 127 join to form a single-piece doped area. Similarly, in the second mesh, the pinch zone 121 joins the box 127 to form another single-piece doped area.

[0122] The transfer grid 117 extends vertically into the substrate 100 from the upper face 100.1. It has a substantially square or rectangular shape when viewed from above. It completely surrounds the detection zone 126. The detection zone 126 extends from one edge of the transfer grid 117 to the other. The housing 127 extends from one edge of a peripheral insulation trench 115 to the other. It surrounds the transfer grid 117.

[0123] Photogenerated electrical charges in a photosensitive region of the intensity pixel 7 are collected in the detection area 126 when the transfer grid 117 is activated. The transfer grid 117 is located directly above this photosensitive region.

[0124] The depth pixel 6 does not share its inverse transfer grid 112 and its pinch grid 114 with a neighboring depth pixel 6. Advantageously, each intensity pixel 7 is separated from a neighboring pixel by an inverse transfer grid 112 and a pinch grid 114 identical to those of the depth pixel 6, and arranged in the same way. Thus, all intensity pixels 7 exhibit identical operating characteristics. The inverse transfer and pinch grids 112, 114 of the first mesh are advantageously polarized by electrical contacts when the sensor is in operation.

[0125] For each intensity pixel 7, the detection area 126 and the transfer grid 117 are connected to a control circuit by, respectively, a read contact 171 and a grid contact 172. The control circuit may be part of the read circuit or an independent circuit. The housings 127 of the intensity pixels 7 of the first mesh are connected to the control circuit by a fifth contact 165. In operation, the housing 127 of the intensity pixel 7 of the second mesh is polarized here via the seventh contact 167 and the pinch area 121.

[0126] By way of example, the sensor can be configured to capture a color image. The intensity 7 pixels of the set of 4 pixels can then each be sensitive in a range of wavelengths of the visible spectrum distinct from the other two intensity 7 pixels in the set. It is possible to combine them with a pixelated filter arranged opposite the underside of substrate 100, so that each pixel is exclusively sensitive to one of the three colors among red, green or blue.

[0127] Specific embodiments have just been described. Various variants and modifications will be apparent to those skilled in the art. The particular arrangement of the transfer and inverse transfer grids, both with each other and with respect to the flow path, is notably an essential element for the bidirectional transfer between the photosensitive region and the memory region, enabling the compactness objective of the invention to be achieved. This can be exploited in pixels of similar depth, connected to other types of read circuits.

Claims

1. Demands An image sensor comprising a readout circuit and a plurality of pixels formed in and / or on a semiconductor substrate (100) of the sensor, such that at least one of the pixels is a depth pixel (5, 6), each depth pixel comprising: • a photosensitive region (120) of the substrate (100), • a controllable storage area including: • a flow path for electrical charges extending vertically in the substrate (100) directly above the photosensitive region (120) and comprising a potential well called the memory region (135) and a potential barrier called the barrier (131) interposed between the memory region (135) and the photosensitive region (120), • a transfer grid (111) extending vertically into the substrate (100) directly above the photosensitive region (120), opposite the barrier (131), • a reverse transfer grid (112) extending vertically into the substrate (100) opposite the barrier (131) and an upper part of the photosensitive region (120), • an additional electrical charge flow path extending vertically in the substrate (100) above the photosensitive region (120) comprising a potential well called a collection zone (125) and a potential barrier, called a collection channel (133), interposed between the collection zone (125) and the photosensitive region (120), • an initialization grid (113) extending vertically in the substrate (100) directly above the photosensitive region (120), opposite the collection channel (133), the reading circuit comprising a reading node (SN) electrically connected to the collection zone (125) and configured to successively: • apply a periodic pulse train to the transfer gate (111) during a sampling phase (T1) so as to flow electrical charges from the photosensitive region (120) to the memory region (135) during the pulses, • initialize the read node (SN), • activate the inverse transfer gate (112) and the initialization gate (113) so as to flow electrical charges from the memory region (135) to the collection area (125) during a charge evacuation phase (T4), • read an electrical potential Vsig from the read node (SN).

2. Sensor according to claim 1, wherein the reading circuit is configured to read an electrical potential Vinit from the reading node (SN) prior to the charge evacuation phase (T4) and subsequent to the initialization of the reading node (SN), the sensor being such that it includes means for performing correlated double sampling from Vinit and Vsig.

3. Sensor according to claim 1 or 2, wherein the flow path of the controllable storage area comprises a pinch zone (121) covering the memory region (135) on one side of the memory region (135) opposite the barrier (131), wherein the controllable storage area comprises a pinch grid (114) extending vertically in the substrate (100) opposite the memory region (135), and wherein the read circuit is configured to apply an electrical potential difference between the pinch zone (121) and the pinch grid (114) so ​​as to passivate the memory region (135) from electrical charges from the pinch zone (121).

4. Sensor according to claim 3, wherein the pinching grid (114) is housed in a notch made in the reverse transfer grid (112).

5. Sensor according to any one of the preceding claims, wherein the reading circuit is further configured to activate the transfer grid (111) during the charge evacuation phase (T4) after activation of the reverse transfer grid (112).

6. Sensor according to any one of the preceding claims, wherein the readout circuit is configured to activate the initialization grid (113) in opposite phase to the transfer grid (111) during the sampling phase (T1).

7. Sensor according to any one of the preceding claims, wherein, for each depth pixel, the transfer grid (111) extends alongside the memory region (135).

8. Sensor according to any one of the preceding claims, wherein, for each depth pixel (5, 6), the barrier (131), the memory region (135) and the collection area (125) are doped with a first type of conductivity, and have concentrations of dopant elements respectively equal to NI, N2, N3 such that NI is strictly less than N2, and N2 is strictly less than N3.

9. Sensor according to claims 3 and 8, wherein, for each depth pixel (5, 6), the pinch zone (121) is doped with a second type of conductivity opposite to the first type of conductivity.

10. Sensor according to claims 8 or 9, wherein the collection channel (133) has a concentration of doping elements equal to NI.

11. Sensor according to any one of claims 8 to 10, wherein, for each depth pixel (5, 6), the transfer grid (111) has a U-shaped top view, surrounding the flow path of the controllable storage area.

12. Sensor according to any one of the preceding claims, wherein the plurality of pixels is arranged in a matrix, wherein each pixel has a peripheral insulation trench (115) extending vertically in a peripheral region of the pixel opposite a photosensitive region of the pixel and wherein the readout circuit is configured to apply a common fixed electrical potential to all peripheral insulation trenches (115).

13. Sensor according to claims 3 and 12, wherein each pinch grid (114) and each inverse transfer grid (112) are arranged in separation planes of two contiguous pixels of the pixel matrix.

14. A sensor according to claim 13, wherein the peripheral insulation trenches (115) form a continuous mesh comprising cells such that each cell surrounds two pixels, and wherein the readout circuit is electrically connected to 27 a peripheral zone of the mesh so as to apply the common fixed electrical potential.

15. Sensor according to any one of claims 12 to 14, wherein all pixels of the matrix have the same size, and wherein the pixel matrix comprises intensity pixels configured to deliver a signal representative of the intensity of an incident luminous flux.

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